This investigation approaches the elucidation of integrative regulation in thebacterial cell. It includes a study of control points that act to coordinate regulatory functions of aminoacyl-tRNA synthetases and control points for pathway enzymes involved in biosynthesis of isoleucine, valine, and leucine. The principal organisms utilized in these studies will be Escherichia coli and Salmonella typhimurium. Specifically, known genetic regions, that are involved in regulation of synthesis of branched-chain amino acid biosynthetic pathway enzymes, will be examined to assess their involvement in regulation of synthesis of the cognate aminoacyk-tRNA synthetases. Conditions of cultivation will be manipulated to obtain varied repression control of pathway enzyme formation. The effect that regulatory varied repression control of pathway enzyme synthesis will simultaneously be assessed. The role of tRNA levels with common repressiion control in normal and mutant strains. In order to discover other potential points or factors of common control, attempts will be made to select mutants having altered regulation of biosynthetic and activating enzyme synthesis. The general procedure for such mutant selections will be will be the use of analogs of the branched-chain amino acids and their intermediated to obtain resistant mutants. The resultant mutants will be screened for excretion properties and by analysis of enzyme synthesis or activating enzyme syntheis will be explored to aid interpretations relating to common control.